Reinforced asbestos paper yarn and method of making same

ABSTRACT

Asbestos yarn is produced by slitting a web of asbestos paper reinforced with spaced, longitudinally extending strands of glass fibers. Each ribbon formed by slitting includes at least one longitudinally extending strand of glass fibers. The ribbons are wetted and twisted to form an asbestos yarn. The yarns are uniform in diameter and suitable for use in dryer felts.

United States Patent 1 Sloane, deceased et al.

REINFORCED ASBESTOS PAPER YARN AND METHOD OF MAKING SAME Inventors: Ivan Henry Sloane, deceased, late of Assignee: Johns-Manville Corporation, New

Filed:

York, NY.

Aug. 13, 1971 Appl. No.: 171,655

US. Cl ..57/140 G, 57/150, 57/160,

' 57/ 165 Int. Cl ..D02g 3/04, D02g 3/ 18, D02g 3/20 Field of Search ..57/5, 6, 7, 31, 32,

| I I PAPER STOCK 1 57/139, 140 BY, 140 G, 140 R, 150, 151,

[451 May 1, 1973 [56] References Cited UNITED STATES PATENTS 1,681,234 8/1928 Heany ..57/165 X 2,217,049 10/1940 Greenleaf.. ...57 /140 UX 2,230,271 2/1941 Simpson .,57/l40 G UX FOREIGN PATENTS OR APPLICATIONS 746,699 3/ 1953 Great Britain ..57/14O G Primary Examiner-Donald E. Watkins Att0rney-John A. McKinney et a1.

[ 5 7] ABSTRACT Asbestos yarn is produced by slitting a web of asbestos paper reinforced with spaced, longitudinally extending strands of glass fibers. Each ribbon formed by slitting includes at least one longitudinally extending strand of glass fibers. The ribbons are wetted and twisted to form an asbestos yarn. The yarns are uniform in diameter and suitable for use in dryer felts.

18 Claims, 1 Drawing Figure PAPER OPERATION WET SECTION DRIER szcnou PREPARATION PAPER FORMATION PAPER MACHINE IPAPER Ia sLnTTmET GLASS FIBER REINFORCEMENT I INSERTION J I I I y I r 1 "-3 T YARN WINDING RESIN TREATMENT CLOTH WEAVING TWISTING JRIBBON AND ADDITIONAL REINFORCING CAN BE TWISTED TOGETHER) REINFORCED ASBESTOS PAPER YARN AND METHOD OF MAKING SAME FIELD OF THE INVENTION This invention relates to an asbestos yarn, and to a method of making such a yarn. More particularly, the invention relates to the production of asbestos yarn by twisting narrow ribbons slit from a web of asbestos paper.

DESCRIPTION OF THE PRIOR ART Asbestos fibers are relatively straight, smooth, and slippery, compared to common organic textile fibers such as cotton, wool, and synthetic fibers, which makes it difficult or impossible for a yarn of 100 percent asbestos fiber to remain bound together during the various manipulations involved in the production of asbestos yarn. Further, asbestos fibers are relatively short and weak, which makes the fabrication of strong yarn, cloth, and fabrics from asbestos a continuing problem. Thus, cotton and other organic fibers have been included in the production of asbestos yarns, although incorporation of such organic fibers tends to decrease the fire and heat resistance of textiles made from such asbestos-organic blends.

Despite numerous attempts to develop alternative yarn forming procedures, fine asbestos yarns are usually commercially manufactured by conventional dry textile manufacturing procedures including carding of the fiber to make card sliver which is later processed to make roving and then yarn. In the production of asbestos yarn, the conventional dry. textile manufactur ing operations generate large quantities of very fine asbestos dust. This dust presents a health problem for employees which is only partially solved by utilizing such economically undesirable techniques as slowing down the carding operation and providing expensive mechanical ventilation equipment.

It has previously been proposed to form asbestos material into paper or paper-like material, and after forming the paper or paper-like material to separate it into strips of suitable width and to wind the strips into flat rolls. Then each strip, preferably in a softened or moistened condition, is drawn from the flat roll under low tension and twisted with one or more supporting or reinforcing filaments to provide strength.

Such procedures have proved feasible for manufacturing relatively coarse asbestos yarn for use in friction, wear, and heat-resisting fabrics suitable, for example, as brake linings, transmission linings, and clutch facings. However, this technique has not previously proved feasible for forming small diameter yarn due to difficulties encountered in forming the thin sheets of asbestos paper required to produce such yarn and rapidly processing such sheets on existing equipment and then slitting them.

Such thin sheets have lacked the integrity required to allow their removal from the paper making apparatus. Special equipment has been required to produce thin asbestos sheets. When these thin sheets were slit into ribbons and softened or moistened to prepare them for the twisting operation, it was found that such ribbons, being in a weakened state due to the softening or moistening, often lacked the cohesiveness or strength required to withstand the forces of twisting which resulted in breakage and/or disintegration of the ribbons. Ribbons produced from thicker sheets for production of relatively coarse asbestos yarn did not exhibit such difficulties.

Some demanding applications require a relatively uniform, fine diameter asbestos yarn. For example, the transverse yarns in paper dryer felts are exposed to high temperatures and yet must not shrink or fail, or an expensive paper making machine suffers a costly period of down time. Further, for efficient drying of the paper, the transverse yarns must be of a small uniform diameter to insure adequate air flow on the entire surfaceof the web of paper.

It would be desirable to produce thin asbestos sheets on existing conventional equipment which have the necessary strength so that they can be slit and twisted into small diameter yarns. Heretofore, manufacturing difficulties and inherent characteristics of the ribbons inhibited the utilization of such non-textile forming procedures. The dry carding procedure, because it is capable of producing fine asbestos yarn, has continued to be used for producing yarn for dryer felts, despite its disadvantages which include the copious production of dust and the non-uniform diameter and strength of fibers produced thereby.

SUMMARY OF THE INVENTION The present invention provides a method of manufacturing small diameter asbestos yarn of improved uniformity. During formation of a water-laid web of asbestos paper, transversely spaced, parallel, longitudinally extending strands of glass fibers are inserted into the web. The web is slit or severed into a plurality of narrow-width ribbons which each contain at least one longitudinally-extending strand of glass fibers, and the narrow-width ribbons are wetted or softened and twisted to form the asbestos yarn.

Incorporation of the longitudinally-extending glass fibers provides the internal reinforcement necessary for handling thin asbestos webs during their formation and maintaining the integrity of ribbons cut from such webs during twisting into yarns while in. the wet and weak state as well as providing strength in final products incorporating such yarns, for example, woven dryer felts.

Preferably, the web is formed from a composition containing at least about percent asbestos fiber, and the thickness of the web is between about 4 to about 12 mils. A wet-strength-imparting synthetic resin additive is desirably incorporated in the composition to aid in preserving the integrity of the wet ribbons during twisting. The composition also desirably includes organic fiber to permit rapid drying, winding, slitting and twisting of the asbestos paper.

The invention further provides an asbestos yarn of improved smoothness and uniformity of diameter comprising a single twisted ribbon of asbestos paper. The ribbon has a width of less than about one-half inch, a thickness of less than about 12 miL, and includes a plurality of layers of water-laid fibers with at least one longitudinally extending strand of glass fibers preferably of 75 s to 's count positioned between a pair of adjacent layers.

The process of this invention is capable of producing a smooth small diameter asbestos yarn of improved uniformity of diameter which is dimensionally stable and longitudinally shrinleresistant and is suitable for use in demanding applications such as paper dryer felts. The yarn is produced by a process which can be practiced on standard asbestos paper making machinery in a rapid, trouble-free manner. The incorporation of glass fibers into the web of asbestos paper as the web is being formed provides the web with good strength properties which enable it to withstand rapid and economical machine processing, to maintain integrity during twisting of ribbons slit from such paper and to provide strength in products incorporating the asbestos yarn.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a schematic illustration of equipment capable of practicing the method of this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In accordance with the present invention, an asbestos yarn is manufactured by first forming a waterlaid web of asbestos paper, and inserting transversely spaced, parallel, longitudinally extending strands of glass fibers into the web as the web is being formed. Preferably, the web forming operation includes beating an aqueous paper stock composition having a solids content comprising at least 90 percent by weight asbestos fiber, 4 to 8 percent by weight of an organic fiber and 2 to 4 percent of a wet strength additive to form a slurry in which the solids are uniformly distributed.

The asbestos fiber preferably is ofa grade including a majority of fibers at least one-fourth inch long. The aqueous paper stock composition should contain at least 90 percent by weight asbestos fiber to insure that the yarn possesses good heat stability.

The organic fiber is added to the aqueous paper stock composition to assist in binding the asbestos fibers together to permit the rapid drying, winding, slitting and twisting of the asbestos paper. Without the organic fiber and the wet strength additive, the paper could not be rapidly dried, wound or slit, and twisting would be almost impossible since the asbestos fiber web would separate from the core of glass fiber strands.

Suitable organic fibers include cotton, papermakers rayon, kraft paper, and the more heat resistant synthetic organic fibers. Preferably, the length of these organic fibers is from one-fourth to one-half inch. Suitable wet strength additives include melamine-formaldehyde resins, acrylic resins sold by B. F. Goodrich under the designation Hycar, and acrylic resins sold by Rohm & Haas under the designation Rhoplex.

The paper stock composition must be a dilute aqueous composition and usually contains from 0.25 to 0.50 percent by weight of solids to permit rapid formation of thin uniform sheets of asbestos paper. The paper stock composition can also optionally include conventional paper making binders such as bentonite and a precipitating agent such as alum.

' The paper stock slurry is deposited on a foraminous surface to permit the water to drain from the solids and thus form a plurality of wet sheets of asbestos paper. A plurality of transversely spaced, longitudinally extending, parallel strands of glass fibers are inserted between a pair of the wet sheets during formation. The formation of the wet sheets of asbestos paper and the insertion of the strands ofglass fiber can conveniently be accomplished using a cylinder paper making machine. In practice, it has been found that the present method can be used on twoto five-roll machines, and that it is generally desirable to insert the strands between the first and second rolls of the cylinder machine. The strands can be inserted between the wet sheets of asbestos paper by feeding the glass fibers through narrow tubes using compressed air. The apparatus for feeding and inserting the glass fibers between the asbestos sheets is similar to that used in inserting glass fibers into asbestos paper utilized as pipeline insulation. The wet sheets formed by the various cylinders are drawn together in a laminar relationship and enclose the strands of glass fibers which have previously been inserted therebetween.

Subsequently, the paper web is dried by passing the web through a conventional dryer section of a paper machine. The presence of the longitudinally extending strands of glass fibers permits rapid processing of the asbestos paper in the wet section and the dryer section of a paper making machine even when the paper is formed as a very thin 4 to 5 mil web having a weight of 1.4'to 1.6 lbs. per square feet.

In accordance with the invention, the dried asbestos paper web is slit into a plurality of longitudinally extending ribbons which each contain at least one longitudinally extending strand of glass fibers. The slitting can be accomplished by conventional web slitting devices which comprise a stationary cutting edge with the web being transported past the cutting edge and passing on each side of it. Altemately, a rotary cutting disc can be used to slit the paper. Preferably, the web is slit to provide ribbons of from about one-fourth to about seven-sixteenths inch wide, because inability to slit uniformly occurs if the ribbons are narrower than one-fourth inch wide and it is not presently possible to twist a ribbon wider than one-half inch without overlapping and causing rough surfaces. Surprisingly, the reinforcing strands of glass fibers can be inserted at the cloesly spaced intervals needed to provide reinforcement in each ribbon without creating excessive breakage problems during the slitting operation.

The narrow-width ribbons are wetted or softened, usually with water, and then twisted to form an asbestos yarn. Preferably, the moisture content of the ribbons is in the 20-40% range at the time of twisting. The twisting can be accomplished by conventional textile twisting equipment. Preferably, a S twist is imparted and the twist per inch varies from 5 to 10.

For applications such as gasket tape, dryer felt, and insulation fabric, further natural or synthetic organic or inorganic reinforcing fibers are preferably added dur ing the twisting operation to provide additional strength to withstand weaving. The nature of the end use determines the specific reinforcing fiber utilized. For dryer felts, a proven heat resistant synthetic fiber such as nylon or polyester is selected. In less severe applications, other fibers such as rayon, cotton, or polyvinyl alcohol can be used.

It is also desirable to apply a protective coating or sizing to the reinforced asbestos yarns in order to provide enhanced performance during weaving and durability in the final fabric. A thermosetting resin, preferablyan acrylic resin or blends of acrylic resins,

are suitable for such purposes. The yarns are coated with the sizing and dried to partially cure the sizing. Thereafter, the yarns are incorporated into a fabric by any conventional means, such as weaving, and the sizing is given a final set, such as by heat-treating the fabric. When these yarns are incorporated. into dryer felts, it is found that the resin coating provides a hydrophobic effect by preventing water from being drawn into the yarns. Dryer felts incorporating these yarns can be dried more rapidly due to lower water contents and in most cases the water can be. merely blown off the fabric by means, for example, of hot air jets.

The following example is presented to provide a more complete understanding of the. invention. The specific techniques, conditions, materials, and proportions set forth are exemplary and should not be con strued as limiting the scope of the invention. All parts and percentages listed in the specification and claims are weight percentages unless otherwise stated.

EXAMPLE A reinforced twisted asbestos yarn is produced using apparatus similar to that illustrated in the drawing. A paper stock is prepared by beating a furnish comprising 900 parts of chrysotile asbestos fiber sold by Johns- Manville under the designation 4TO4; 60 parts of paper makers rayon (3 denier, /2 inch long staple); parts of bentonite (Grade A ground bentonite from mica pellets); 5 parts alum; and parts ofa wet strength additive (a melamine formaldehyde, resin availableunder the designation Paramel HE. No. .2 fromCyanamid of Canada). A thin web of glass fiber-reinforced asbestos paper having a thickness of 5.5 mils is produced using two cylinders of a five cylinder paper making machine and inserting longitudinally within the web 1504/0 glass fiber strands (ECG Fibreglas Filament yarn from Fibreglas Canada Ltd.) at 4 inch intervals. At a machine speed of 68 feet per minute, this procedure gave excellent sheet formation with very good handling properties.

The asbestos paper web is dried and wound into a roll with no problem of wrinkling in the dryers, or in the winding operation. The roll of wound asbestos paper is unwound and slit by moving it past a slitter which slits the web into ribbons having an average width of fivesixteenths inch. The resulting ribbons of asbestos paper have at least one reinforcing strand of glass fibers and contain 93 percent asbestos, weigh 1.8 2.0 pounds per hundred square feet, have an average thickness. of 5.5 mils, and an average tensile strength of 13 pounds.

The ribbons are wetted with water and twisted with polyester fiber to impart an S twist to the composite yarn. Subsequently the twisted yarn is surface treated with a composition comprising thermosetting acrylic resins and water, made up of 5 parts of Acrysol 2004 (36 percent solids), 3 parts of Acrysol 2003 (36 per cent solids) and 2 parts water. Acrysol resins are thermosetting acrylic resins manufactured by Rohm & Haas. The surface treatment deposits about 13 percent by weight (based on the weight of the yarn subjected to the surface treatment) of resin solids on the yarn.

The resulting resin-treated yarn is uniform in diameter, longitudinally shrink-resistant, smooth and suitable for dryer felt manufacture.

The inventionin its broader aspects is not limited to the specific details shown and described, and departures may be made from such details without departing from the principles of the invention, and without sacrificing its chief advantages.

What is claimed is:

1. An improved method of manufacturing asbestos yarn comprising:

a. forming a water-laid web of asbestos paper, and inserting transversely spaced, parallel, longitudinally extending strands of glass fibers into the web as the web is being formed;

b. slitting the web into a plurality of narrow-width ribbons, each of which contains at least one longitudinally extending strand of glass fibers; and

c. twisting the wetted ribbons to form an asbestos yarn.

2. The method of claim 1 in which the narrow-width ribbons have a width of less than about one-half inch and in which the thickness of the web is less than about 12 mils.

3. The method of claim 2 in which the web is formed from a composition containing at least about percent asbestos fiber.

4. The method of claim 1 including the step of wetting the narrow-width ribbons prior to twisting the ribbons into yarn.

5. The method of claim 4 in which the web is formed from a composition including a wet strength additive to preserve the integrity of the wet ribbon during twisting.

6. The method of claim 5 in which the wet strength additive is a melamine formaldehyde resin.

7. The method of claim 4 in which the narrow-width ribbons have a width between about one-fourth and about seven-sixteenths inch and in which the thickness of the web is between about 4 to about 12 mils.

8. The method of claim 1 in which reinforcing fibers are twisted with the narrow-width ribbons to form a composite yarn.

9. The method of claim l in which the twisted yarn is subsequently coated with asizing composition.

10. The method of claim 9 wherein the sizing composition comprises a thermosetting resin and the yarn is heated to partially cure the resin.

11. The method of claim 10 wherein said thermosetting resinisan acrylic resin.

12. A method of manufacturing asbestos yarn comprising:

a. beating an aqueous composition having a solids content comprising at least 90 percent by weight asbestos fiber, 4 to 8 percent by weight of an organic fiber and 2 to 4 percent ofa wet strength additive to form a slurry in which the solids are uniformly distributed;

b. depositing the slurry on a moving foraminous surface to form a plurality of wet. sheets of asbestos paper;

c. inserting a plurality of transversely spaced, longitudinally extending, parallel strands of glass fibers between a pair of wet sheets;

d. drawing the sheets together in a laminar relationship to form a paper web;

e. drying the web and thereafter slitting the web into a plurality of longitudinally extending ribbons each of which contains at least one longitudinally extending strand of glass fibers, the ribbons being from about one-fourth to about seven-sixteenths inch wide and between about 4 to about 12 mils thick; and g f. vwetting'the narrow-width ribbons and twisting the wetted ribbons to form an asbestos yam.

13. An asbestos yarn of improved uniformity of diameter comprising: a twisted ribbon of asbestos paper, said ribbon having a width of less than about one-half inch, a thickness ofless than about 12 mil, and including a plurality of layers of water-laid fibers with at least one longitudinally extending strand of glass fibers positioned between a pair of adjacent layer.

14. The asbestos yarn of claim 13 further including reinforcing fiber twisted with the ribbon of asbestos paper. I

15. The asbestos yarn of claim 13 further including a coating of a thermosetting resin.

16. The asbestos yarn of claim 15 wherein said thermosetting resin is an acrylic resin.

17. The asbestos yarn of claim 13 wherein said asbestos paper includes at least percent asbestos fiber.

18. The asbestos yarn of claim 13 wherein said ribbon has a width of between about one-fourth to about seven-sixteenths inch and a thickness of between about 4 to about 12 mils. 

2. The method of claim 1 in which the narrow-width ribbons have a width of less than about one-half inch and in which the thickness of the web is less than about 12 mils.
 3. The method of claim 2 in which the web is formed from a composition containing at least about 90 percent asbestos fiber.
 4. The method of claim 1 including the step of wetting the narrow-width ribbons prior to twisting the ribbons into yarn.
 5. The method of claim 4 in which the web is formed from a composition including a wet strength additive to preserve the integrity of the wet ribbon during twisting.
 6. The method of claim 5 in which the wet strength additive is a melamine formaldehyde resin.
 7. The method of claim 4 in which the narrow-width ribbons have a width between about one-fourth and about seven-sixteenths inch and in which the thickness of the web is between about 4 to about 12 mils.
 8. The method of claim 1 in which reinforcing fibers are twisted with the narrow-width ribbons to form a composite yarn.
 9. The method of claim 1 in which the twisted yarn is subsequently coated with a sizing composition.
 10. The method of claim 9 wherein the sizing composition comprises a thermosetting resin and the yarn is heated to partially cure the resin.
 11. The method of claim 10 whErein said thermosetting resin is an acrylic resin.
 12. A method of manufacturing asbestos yarn comprising: a. beating an aqueous composition having a solids content comprising at least 90 percent by weight asbestos fiber, 4 to 8 percent by weight of an organic fiber and 2 to 4 percent of a wet strength additive to form a slurry in which the solids are uniformly distributed; b. depositing the slurry on a moving foraminous surface to form a plurality of wet sheets of asbestos paper; c. inserting a plurality of transversely spaced, longitudinally extending, parallel strands of glass fibers between a pair of wet sheets; d. drawing the sheets together in a laminar relationship to form a paper web; e. drying the web and thereafter slitting the web into a plurality of longitudinally extending ribbons each of which contains at least one longitudinally extending strand of glass fibers, the ribbons being from about one-fourth to about seven-sixteenths inch wide and between about 4 to about 12 mils thick; and f. wetting the narrow-width ribbons and twisting the wetted ribbons to form an asbestos yarn.
 13. An asbestos yarn of improved uniformity of diameter comprising: a twisted ribbon of asbestos paper, said ribbon having a width of less than about one-half inch, a thickness of less than about 12 mil, and including a plurality of layers of water-laid fibers with at least one longitudinally extending strand of glass fibers positioned between a pair of adjacent layer.
 14. The asbestos yarn of claim 13 further including reinforcing fiber twisted with the ribbon of asbestos paper.
 15. The asbestos yarn of claim 13 further including a coating of a thermosetting resin.
 16. The asbestos yarn of claim 15 wherein said thermosetting resin is an acrylic resin.
 17. The asbestos yarn of claim 13 wherein said asbestos paper includes at least 90 percent asbestos fiber.
 18. The asbestos yarn of claim 13 wherein said ribbon has a width of between about one-fourth to about seven-sixteenths inch and a thickness of between about 4 to about 12 mils. 